1. Field of the Invention
The present invention relates to signal processing systems and methods. Specifically, the present invention relates to improvements in photonically assisted wide-band RF filtering using optical components.
2. Background of the Invention
RF Signal processing over a wide accessible bandwidth is an unsolved problem. When dealing with filtering 50 MHz resolutions over a range of 10 GHz-200 GHz, individual RF processing components cannot cover this operating range and do not have the agility required for many high-speed filtering applications. FIG. 1 shows a representative wideband RF signal 101 having regions of interest 105.
The conventional method of accessing the information in regions 105 is to digitize a large portion of signal 101 and process it electronically. Present limitations include the bandwidth of the electronics used in the processing apparatus, and the resolution of analog to digital conversion at these speeds, both of which lead to problems as the frequency range gets higher. Further, although the desired bandwidth may be a reasonable fraction of the overall bandwidth, in the analog domain different electronic components are required as the working frequency is changed. For instance, RF components operating at 1 GHz look quite different from RF components operating at 20-60 GHz. A unique setup has to be used for varying ranges, leading to increased cost and complexity.
One present solution involves filtering the signal. An analog operation is performed on this wide RF spectrum, narrowing it to a region of interest, and then processed by the digital signal processor. FIG. 2A shows such a conventional RF front-end filter. The filter has a specific bandwidth it operates on. To work on a different frequency, significant aspects of the filter must be changed.
FIG. 2B shows a system block diagram of an RF signal processing system, and the aspect of the system to which the present invention (dashed area) is applied. Optical processing techniques have previously been discussed as promising ways to address many of the limitations of conventional electronic processing methods. These methods have fallen short due to limitations in performance, including agility, dynamic range, size, weight, power, and ability to realize essential filter functions in a stable manner.
In contrast to conventional RF signal processing systems, in which filter operations can be based on the electric field intensity, optical RF signal processing systems have been long restricted from using electric field-based processing techniques, due to concerns about stability. See, for example: Capmany, J., Ortega, B., Pastor, D., IEEE Jnl. Lightwave Tech., v. 24, no. 1, pp. 201-229, February 2006., and Minasian, R. A., IEEE Trans. Microwave Theory and Techniques, v. 54, no. 2, pp. 832-846, February 2006.), This limitation is a significant shortcoming. Further F shortcomings related to the dynamic range of electrical to optical (E/O) conversions also exist. An improved method and system for photonically assisted RF filtering is needed.